Consolidation and Swelling Processes in Unsaturated Soils - Unsaturated Soil Mechanics in Engineering Practice - page 852

2.5

No evaporation
Evaporation on surface

2.0

1.5

1.0

0.5

0.0

0.1 1 10 100 1000 10,000

Time ( t ) (min)

Figure 16.63 Computed deflection versus time for free-swell oedometer test with and without
evaporation from surface of soil specimen.

20

5300 min

120 min

16

12

8

t = 4 min
t = 30 min
t = 120 min
t = 5300 min

30 min

4

4 min

0

0 500 1000 1500 2000 2500 3000

Matric suction ( u a - u w ) (kPa)

Figure 16.64 Computed matric suction profiles for free-swell oedometer test with evaporation
from surface of specimen.

however, the rheological models can serve a role as a visu-
alization tool.
It was shown in the previous chapter that two linear rhe-
ological models connected in series can be used to simulate
instantaneous and time-dependent processes in an unsatu-
rated soil. One linear model simulates the solid phase com-
bined with the water phase while a second linear model
simulates the solid phase combined with the air phase. The
two rheological models can be connected in series to sim-
ulate the time-dependent behavior (i.e., consolidation and
swelling) of a layer of unsaturated soil.
The total stress applied to the two linear rheological
models connected in series acts equally on both elements
and represents the role of the two independent stress state
variables, σ

conservative energy requirement (i.e., σ = σ H + σ M , where

σ M = stress on the Maxwell portion of the linear element,

σ H stress on the Hookean portion of the linear element

which represents either the pore-water pressure u w or the
pore-air pressure u a and σ

=

= total stress applied to the

linear element).
The total strain ε is equal to the sum of the strain in
the linear element associated with the σ

u w stress state
variable ε w and the strain in the linear element associated
with the σ

−

ε a ).
The Hookean portion and the Maxwell portion of each
linear rheological element must always deform equal
amounts

− u a stress state variable ε a (i.e., ε = ε w +

16.11.1 Constitutive Relations for Rheological Model
Let us first consider the linear rheological element associ-
ated with the stress state variable σ

u a . The stress in the Maxwell
and Hookean portions of each linear element must always
add to the total stress applied. This condition satisfies the

− u w and σ −

− u w . The total stress